1. Field of the Invention
The invention is directed to a method for optimizing the workload on connection sections for ABR traffic having ATM cells belonging to ABR traffic that are transmitted between a transmitter and a receiver via common connection sections in which control cells are inserted into the stream of ATM cells that are taken by the receiver and returned to the transmitter.
2. Description of the Related Art
A plurality of connection types have been defined for connections via which information are transmitted according to an asynchronous transfer mode (ATM). These connections types may be classified as: 1) connections with which information are transmitted with a constant bit rate (CBR) are 2) connection with via which information are transmitted with (VBR).
Connection types may also be classified as connections with which information are transmitted with an available bit rate (ABR). The latter involve connections via which information having low priority are transmitted between a transmitter and a reciever.
To achieves this, control cells are inserted in a time grid into the stream of ATM cells belonging to a connection sent out by the transmitter. As a rule, this is the case at approximately every thirty second ATM cell. The ATM cells are then supplied to the reciever, into consideration together with the control cells. The latter takes the ATM cells bearing the payload information from the cell stream. Additionally, the control cells are taken and sent back to the transmitter together with call-associated data as well as data describing the current condition of the connection sections. From there, the connection-associated information are taken from the control cells and the transmission rate is potentially reduced.
European Patent Application EP 0 719 012 A discloses a method for traffic steering and overload defense for packet-oriented networks. A virtual connection between a source node and a destination node via which ATM cells are routed is set up between these nodes. When the resources of a virtual connection are not fully utilized, the transmission rate is raised. When the resources of a virtual connection lie beyond the capacity limit of the transmission path, the transmission rate is reduced. The dynamics of the transmission event is deteriorated since the measuring of the ATM cells occurs within a fixed time span.
The publication, xe2x80x9cA Multi-Level Explicit Rate Control Scheme for ABR Traffic with Heterogeneous Service Requirementsxe2x80x9d, Jxc3x6rg Liebeherr et al., Proceedings of the 16th Int. Conf. on distributed computing systems, Hong Kong, May 27-30, 1996, No. 16, pp. 570-577, likewise discloses a method for overload defense given ABR traffic, and mentions theoratical considerations about a multi-stage method that cannot be transferred to practical conditions without further effort. The presents specification does not address how the measuring of the ATM cells belonging to ABR traffic is to ensue, however.
Finally, the publication, xe2x80x9cOn End System Behavior for Explicit Forward Congestion Indication of ABR Service and Its Performancexe2x80x9d, Arata Koike et al., IEICE Transactions on communications, Vol. E79-B, No. 4, Apr. 1, 1996, pp. 605-610, likewise yields a method for overload defense in ABR traffic. Here, too, theoretical considerations based on simulations are provided that can likewise not be transferred to practical, conditions without further effort. The present specification does not address how the measuring of the ATM cells belonging to ABR traffic should ensue, however.
The proposal to the ATM Forum 96-1172 proposes that ATM cells belonging to ABR traffic be controlled according to the criterion of a predetermined algorithm (ERICA). The present specification does not address how this is to be implemented under practical conditions, however, is not addressed here.
The invention is based on the object of disclosing a way of controlling ATM cells belonging to ABR traffic in an efficient way.
This is achieved by a method having steps of measuring a the frequency of occurrence of ATM cells in a connection-associated manner during a transmission in a forward transmission direction, producing a measured result, measuring further parameters, triggering a control procedure by the step of measuring a frequency of occurrence, supplying the measured frequency result to a control procedure together with further, measured parameters, thus producing a calculated rate value, entering the calculated rate value by the control procedure into the control cells transmitted in the return transmission direction if the calculated rate value is greater than a rate value carried along in said control cells, and adapting the transmission rate in the transmitter to the rate value contained in the control cells if the rate value contained in said control cells is different from an original rate value stored in said transmitter.
Measuring the frequency of occurrence of the ATM cells belonging to ABR traffic is particularly advantageous in the invention. According to the criterion of measuring further parameters, these measurements are then subjected to a control procedure. The result of these calculations is inserted into the information part of the return-transmitted control cells.
Advantageous developments of the invention are discussed below.
The invention also provides that the other measured parameters are direct, connection-associated parameters that are a measure for the current filling level of the waiting list, the current filling level of the scheduler block, as well as the current filling level of the parameters calculated as sum of the scheduler blocks. This yields the advantage that a current image of the connection is present in the switch. The term xe2x80x9cscheduler blockxe2x80x9d defines a group of connections via which ATM cells are respectively conducted and are multiplexed onto a single connection section or virtual path with a predetermined peak bit rate.
The invention also provides that the other measured parameters are indirectly connection-associated parameters that are a measure for the momentary rate that the scheduler block has used for all ABR connections of the appertaining scheduler block and/or that are a measure for the momentary rate that would be free for the sum of all ABR connections of the appertaining scheduler block.
The invention also provides that the result of the measurement of the frequency of occurrence of the ATM cells, together with the other measured parameters, is stored after the measuring procedure in at least one input waiting list before they are supplied to the control procedure as input parameters.
The invention also provides that the result of the control procedure is stored in a first waiting list, is subsequently converted into an exponential format and is entered into the control cells. The conversion into an exponential format yields the advantage that an especially efficient storing of the identified value can be implemented. The storing of the result of the control procedure in the first waiting list yields the advantage that potentially occurring speed fluctuations of the control procedure can be compensated.
The invention also provides that the ATM cells are briefly stored in a second waiting list during the measuring procedure, in order to be able to implement a read event of the VCI/VPI number stored in the information part of an ATM cell. This advantageously allows co-utilizing the storing required for the statistical multiplexing for the measuring procedure.